#include<bits/stdc++.h>
using namespace std;
#define int __int128
#define endl '\n'
inline int read(){
	int x=0,k=1;char c=getchar();
	while(c<'0'||c>'9'){
		if(c=='-')k=-1;
		c=getchar();
	}
	while(c>='0'&&c<='9')x=(x<<3)+(x<<1)+(c^48),c=getchar();
	return x*k;
}
const int N=1e6+5;
const long double eps=1e-13;
long double p[N];
int n;
struct node{
	long double p;
	int c;
}a[N];
bool cmp(node x,node y){
	return x.p>y.p;
}
void sol(){
	n=read();
	for(int i=1;i<=n;++i){
		cin>>a[i].p;
		a[i].c=read();
	}
	sort(a+1,a+1+n,cmp);
	int sx=0;
	long double ans=0;
	int r=n;
	int sy=0;
	long double y=1;
	for(int i=1;i<=n;++i){
		while(i>r){
			sy-=a[r+1].c;
			y=1/(1-a[r+1].p);
			++r;
		}
		sx+=a[i].c;
		if(a[i].p==a[i+1].p)continue;
		long double x=1/a[i].p;
		while(r>i){
			int rr=r;
			int ssy=sy+a[r].c;
			while(rr-1==rr)ssy+=a[--rr].c;
			long double yy=1/(1-a[rr].p);
			if(ssy-max(sx*x,ssy*yy)>sy-max(sx*x,sy*y))sy=ssy,y=yy,r=rr-1;
			else break;
		}
		ans=max(ans,sx+sy-max(sx*x,sy*y));
	}
	printf("%.10Lf\n",ans);
}
signed main(){
	int T=1;
	while(T--)sol(); 
}